The Doppler waveform of blood flow through the normal fetal pulmonary artery shows a "spike and dome" pattern, with a short, sharp rise during the acceleration phase followed by a dome-shaped period of decreasing flow.
acceleration time to ejection time ratio (AT/ET) =
= (time from onset to peak blood flow in milliseconds) / (time from onset to end of systolic blood flow in milliseconds)
where:
• The time form onset to peak flow goes from minimal to maximal flow (top of spike).
• The values do not appreciably change from 20 to 30 weeks of gestation.
• The presence of congenital malformations or technical difficulties may limit the examination to only one pulmonary artery.
|
Pulmonary Artery
|
mean AT/ET ratio
|
mean AT/ET ratio - 2 standard deviations
|
|
left
|
0.15
|
0.11
|
|
right
|
0.17
|
0.13
|
Pulmonary hypoplasia was associated with:
(1) a low AT/ET ratio in both pulmonary arteries (if both obtainable)
(2) a low AT/ET ratio in one pulmonary artery (if only 1 side obtainable)
All infants with a normal AT/ET ratio in the pulmonary artery from at least one side survived.
Performance:
• The initial data showed a positive and negative predictive value of 100% respectively. This was conducted in 160 normal fetuses and 17 fetuses with congenital anomalies.
